This invention claims priority of the German patent application 100 42 140.7 which is incorporated by reference herein.
The invention concerns an illumination and imaging device for multiple spectral regions. The invention furthermore concerns a coordinate measuring machine having an illumination and imaging device for multiple spectral regions.
In the production of semiconductor chips, as the packing density becomes greater and greater, the pattern widths of the individual patterns become increasingly small. Corresponding to the smaller and smaller patterns, demands in terms of the specifications of coordinate measuring machines, which are used as measurement and inspection systems for measuring the edges of patterns and the position of patterns and for measuring pattern widths, are also increasing. Optical sensing methods continue to be favored in the context of these coordinate measuring instruments, although pattern widths are already smaller than the light wavelength used for measurement or inspection. The reason is that measurement systems with optical sensing methods are substantially easier to use than systems which sense differently, for example using electron beams.
Because the patterns being measured are becoming ever smaller, however, requirements are increasing in terms of not only the properties of the optical system used but also the properties of an illumination and imaging device used for evaluation and analysis.
A coordinate measuring machine is disclosed in German Unexamined Application DE-A-198 19 492. Illumination of the specimen in incident light is accomplished by way of a light source in the near UV spectral region. Also provided, for detection, is a detector device whose imaging beam path is coupled via a beam splitter into the optical axis defined by an objective. This system does not permit simultaneous illumination and analysis of the specimen under examination using multiple spectral regions, or evaluation on the basis of separate spectral regions.
It is the object of the invention to create an illumination and imaging unit that is suitable for multiple spectral regions.
The stated object is achieved by an illumination and imaging unit having
an objective that defines an optical axis;
a beam splitter module that is arranged in the optical axis;
a plurality of light sources, from each of which an illuminating beam path proceeds; and
a plurality of detectors, associated with each of which is an imaging beam path, the illuminating beam paths and imaging beam paths having a common optical path segment in which the beam splitter module is arranged.
A further object of the invention is to create a coordinate measuring machine that is suitable for measuring very fine patterns on a specimen, and in that context for irradiating the specimen under examination with multiple spectral regions.
The stated object is achieved by a coordinate measuring machine comprising:
an illumination and imaging device for multiple spectral regions, that defines an optical axis; and
a displaceable measurement stage, interferometrically measurable perpendicular and relative to the optical axis, for reception of a specimen.
One advantage of the invention is that the illumination and imaging device is equipped with a beam splitter module that is arranged in the optical axis of the objective used for imaging the specimen under examination. All the imaging and illuminating beam paths are guided along the optical axis. In addition, multiple light sources, from each of which an illuminating beam path proceeds, are provided. The light sources can be configured in such a way that they emit light in a very specific wavelength region. As already mentioned, multiple detectors, with each of which an imaging beam path is associated, are also provided, the illuminating beam paths and imaging beam paths having a common optical path segment in which the beam splitter module is arranged. As a result, the different detectors can each selectively be impinged upon with different wavelength regions.
It is also particularly advantageous to utilize the illumination and imaging device in a coordinate measuring machine. The coordinate measuring machine must be designed so that all possible interfering influences which interfere with a highly accurate measurement are for the most part excluded. Only then is it possible to measure the position of edges on patterns with an accuracy of a few nanometers. With the illumination and imaging device according to the present invention, despite the presence of multiple light sources and detectors it is not necessary to make switchovers or to initiate a mechanical displacement of the optical path segment. These operations would generate turbulence or heat, influencing the measurement in undefined fashion. The use of the beam splitter module in the illumination and imaging device makes it possible for all the illuminating and imaging beam paths to pass through only one objective. The illumination and imaging device is suitable for multiple spectral regions.
One embodiment of the illumination and imaging device proves to be particularly advantageous for very accurate measurement using the coordinate measuring machine. Here there is arranged after the objective a respective beam splitter module having four beam splitters, each arranged in paired fashion in a beam splitter group. In each group, the first beam splitter is a fifty/fifty splitter and the second beam splitter is a dichroic splitter. The properties of the beam splitters in terms of wavelength are such that the first beam splitter group allows own light of a wavelength above a first wavelength xcex1 to pass, and the second beam splitter group allows only light of a wavelength below a second wavelength xcex2 to pass. In addition, behind the second group a detector is arranged after the beam splitter module in the transmitted beam path; the detector detects in the wavelength region between xcex1 and xcex2. The aforesaid three different spectral regions are thereby available. In order to achieve a corresponding high-quality image, the objective is corrected in diffraction-limited fashion in the region between a lower wavelength xcexmin that is smaller than xcex1 and an upper wavelength xcexmax that is greater than xcex2. In the preferred exemplary embodiment, the wavelengths are xcexmin=365 nm and xcexmax=900 nm.